The present invention relates, in general, to molding compositions with a base of an acrylonitrile butadiene styrene copolymer (ABS copolymer) and/or acrylonitrile styrene butyl acrylate copolymer (ASA copolymer) and a styrene acrylonitrile copolymer (SAN copolymer) having an increased chemical resistance and, in particular, a chemical resistance under increased stress.
ABS copolymer and/or ASA copolymer compositions are widely used for the manufacture of molded objects, in particular, housings, for example, electric razor housings.
In applications such as electric razor housings, objects molded from these compositions can be placed in contact with various chemical products, for example, alcohols and bornyl acetate generally contained in shaving lotions and aftershaves.
Objects molded from classic ABS and/or ASA copolymers are generally severely attacked by numerous chemical products such as acids like acetic acid, butyric acid, and nitric acid, phthalates like dioctyl phthalate, gasoline, greases, inks, iodine, alcohols like methyl alcohol, motor oils, phenols, glycols, tetrachloroethylene, [and] acetates like ethyl acetate, amyl acetate, and bornyl acetate.
Thus the object of the present invention is molding compositions with a base of ABS and/or ASA copolymers and an SAN copolymer permitting molded pieces having an increased chemical resistance to be obtained and, in particular, a chemical resistance under increased stress, without adversely affecting the other mechanical properties of the molded pieces.
According to the invention, a molding composition is furnished comprising a mixture that consists of at least one ABS copolymer and at least one ASA copolymer and an SAN copolymer, characterized in that the SAN copolymer has an acrylonitrile concentration (CAN) greater than or equal to 43% by weight and is present in the copolymer mixture in a quantity such that:
the total acrylonitrile concentration (TCAN) of the copolymer mixture is at least 30% by weight in relation to the total weight of the copolymer mixture when the mixture does not contain an ASA copolymer; and
the total acrylonitrile concentration (TCAN) is at least 28% by weight in relation to the total weight of the copolymer mixture when at least one ASA copolymer is present in the copolymer mixture.
The SAN copolymers that are suitable for the present invention must have an acrylonitrile concentration of at least 43% by weight, and preferably greater than 43%. In general, the acrylonitrile concentration of the SAN copolymer will be such that 43% by weightxe2x89xa6CANxe2x89xa647% by weight.
Quite obviously, the SAN copolymer according to the invention can be a mixture of SAN copolymers having the required acrylonitrile concentration. The preferred SAN copolymer is a copolymer having an acrylonitrile concentration of approximately 45% by weight.
As indicated above, when the copolymer mixture only consists of at least one ABS copolymer and at least one SAN copolymer according to the invention, the quantity of SAN copolymers must be such that the total acrylonitrile concentration in the mixture is at least 30% by weight, [and] preferably 31% or more by weight. In general, in this case, the total acrylonitrile concentration in the mixture will be on the order of 31 to 35% by weight.
Likewise, when the copolymer mixture consists of a mixture of at least one ASA copolymer and an SAN copolymer according to the invention, or a mixture of at least one ABS copolymer, at least one ASA copolymer, and an SAN copolymer according to the invention, the total acrylonitrile concentration of the mixture must be at least 28% by weight. Preferably, the total concentration is greater than 28% by weight and generally will be on the order of 30 to 35% by weight.
The acrylonitrile concentrations of the ABS and ASA copolymers are data that are generally furnished by the manufacturers or that can be easily determined. The acrylonitrile concentration of these copolymers is generally from 10 to 30% by weight and classically is on the order of 12% by weight.
In the compositions according to the invention, ABS or ASA copolymers having acrylonitrile concentrations of approximately 10 to 20% by weight are preferably used.
Thus, knowing the acrylonitrile concentrations of the ABS and/or ASA copolymers, a person skilled in the art can easily determine the quantity of SAN copolymers necessary to achieve the total acrylonitrile concentration required for the formulated composition.
However, the compositions according to the invention will generally contain 30 to 70% by weight, [and] preferably 30 to 50% by weight, of ABS and/or ASA copolymers and 30 to 70%, [and] preferably 50 to 70% by weight of SAN copolymers according to the invention.
ABS copolymers, such as ABS graft copolymers, and ASA copolymers are materials that are well known in the technology and are available on the market.
The compositions according to the invention can also contain all adjuvants classically used, such as antioxidants, internal or external lubricants, pigments, dyes, flame retardants, antistatic agents, UV stabilizers, coupling agents, impact strength modifiers, and extenders and/or reinforcing fillers.
These adjuvants are used in the classic proportions.